1. Field of the Invention
The present invention relates generally to a transmission/reception apparatus and method. More particularly, the present invention relates to a transmission/reception apparatus and method for channel estimation in a mobile communication system for transmitting packet data based on a Frequency Division Multiple Access (FDMA) scheme.
2. Description of the Related Art
An Orthogonal Frequency Division Multiple Access (OFDMA) scheme, which is one of recently, widely used multiple access schemes, is a kind of FDMA scheme. An OFDMA system is a system for supporting a multiple access through different sub-carriers using a plurality of orthogonal sub-carriers.
FIG. 1 is a diagram for describing a conventional case where each of a pilot channel, a packet data channel, and a packet data control channel are carried on different sub-carriers in a mobile communication system for transmitting packet data using the OFDMA scheme. In FIG. 1, the packet data channel denotes a physical channel through which a user packet is transmitted, and the packet data control channel denotes a channel for transmitting control information required to demodulate the packet data channel. Hereinafter, the packet data channel is called a data channel, and the packet data control channel is called a control channel.
Referring to FIG. 1, a horizontal axis indicates a time axis, and a vertical axis indicates a frequency axis. Transmission Time Interval (TTI) 101 indicates a time unit in which data is transmitted, and reference numeral 102 indicates a single sub-carrier. Black colored portions indicate sub-carriers on which pilot signals are carried, wherein the sub-carriers constitute a single pilot channel. Hatched portions indicate sub-carriers on which control signals are carried, wherein the sub-carriers constitute a single control channel. White colored portions indicate sub-carriers on which data signals are carried, wherein the sub-carriers constitute a single data channel.
FIG. 2 is a flowchart illustrating a conventional method of receiving packet data in a receiver of a communication system providing a packet data service using the FDMA scheme.
Referring to FIG. 2, the receiver receives a pilot channel in step 111 and estimates a wireless channel using the received pilot channel in step 112. The receiver performs a predetermined equalization process using the obtained channel estimation information and demodulates a control channel in step 113. A predetermined Cyclic Redundancy Check (CRC) test is performed for the demodulated control channel. If a result of the CRC test is invalid in step 114, the receiver returns to step 111 to receive a pilot channel during a subsequent TTI. If the result of the CRC test is valid in step 114, the receiver determines in step 115 whether a data channel has been received. The determination in step 115 is commonly performed using a terminal identification (ID) included in control information included in the control channel. Table 1 illustrates by way of example, the control information included in the control channel.
TABLE 1Control information included in control channelNumber of allocated bitsTerminal ID10Size of data information6Modulation and Coding Scheme (MCS)5informationInformation about used resources5(or resource allocation information)
In Table 1, the terminal ID indicates an indicator previously defined between a base station and terminals to identify the terminals. The size of data information indicates the number of data bits transmitted during a predetermined TTI. The MCS information indicates which modulation method (e.g., Quadrature Phase Shift Keying (QPSK), 8 Pulse Shift Keying (8PSK), 16 Quadrature Amplitude Modulation (16QAM), 64QAM, and so forth) and which coding method (e.g., convolutional coding, turbo coding, and so forth) are used to transmit the data channel. The information about used resources (or resource allocation information) indicates an amount of wireless resources used to transmit the data channel. For example, the information about used resources includes information regarding sub-carriers used to transmit the data channel, the number of sub-carriers, and position information of the sub-carriers. Since the control information illustrated in Table 1 is only an example, the contents of the control information and/or the number of bits can be changed.
By detecting the terminal ID from among the control information illustrated in Table 1, which has been obtained in step 113, the receiver can determine in step 115 whether a data channel has been received thereto. If the receiver determines that the detected terminal ID is the same as an ID previously allocated thereto, the receiver determines in step 115 that ‘data has been transmitted thereto during a current TTI’. If the receiver determines that the detected terminal ID is different from the ID previously allocated thereto, the receiver determines in step 115 that ‘data has not been transmitted thereto during the current TTI’. If the receiver determines in step 115 that ‘data has not been transmitted thereto during the current TTI’, the receiver returns to step 111 to receive a pilot channel during a subsequent TTI. If the receiver determines in step 115 that ‘data has been transmitted thereto during the current TTI’, the receiver demodulates the data channel in step 116. An equalization process is then performed to demodulate the data channel, wherein the information obtained in step 112 is used as channel estimation information required for the equalization process.
As described above, the conventional equalization process for data channel demodulation is performed in the receiver of the FDMA communication system, and channel estimation information required for the equalization process is obtained from only a pilot channel. Thus, the accuracy of the channel estimation information affects the data channel demodulation. If a number of sub-carriers used to transmit the pilot channel is small, or if an amount of power allocated to transmit the pilot channel is small, it is difficult to expect correct channel estimation in the receiver. If the number of sub-carriers used to transmit the pilot channel increases, or if the amount of power allocated to transmit the pilot channel increases, a possibility that correct channel estimation information can be obtained increases. However, if the number of sub-carriers used to transmit the pilot channel increases, or if the amount of power allocated to transmit the pilot channel increases, the number of sub-carriers or power, which can be allocated to other physical channels, i.e., the data channel and the control channel, decreases, resulting in a decrease of a data rate of the data channel.
Accordingly, a need exists for a system and method for minimizing a number of sub-carriers and an amount of transmission power allocated to a pilot channel and increase a channel estimation performance.